Fig 7.

Effects of the K58I mutation on virulence, replication, and contact transmission of H5N1 influenza virus in ferrets. (A and B) Ferrets (n = 5) were inoculated with 0.5 ml PBS containing 10³ TCID₅₀ of the WT or HA2-K58I viruses. Two of the 5 directly inoculated ferrets and all contact ferrets (n = 4) were observed for (A) weight loss and (B) survival. (C) Virus replication in the nasal cavities. Nasal washes were collected from all ferrets on the indicated days until death or termination of the experiment. On day 5, 3 of the 5 directly inoculated ferrets were euthanized to collect tissues, and on days 5 and 6, one ferret each from the WT and the HA2-K58I group, respectively, died from illness. (D) Replication of the WT and HA2-K58I viruses in different body tissues on day 5 after infection. The detection limit was 1 log₁₀ TCID₅₀/ml. Closed symbols indicate directly inoculated ferrets. Open symbols indicate contact ferrets. NC, nasal cavities; T, trachea; LU, left lung's upper lobe; LL, left lung's lower lobe; RU, right lung's upper lobe; RM, right lung's middle lobe; RL, right lung's lower lobe; B, brain; L, liver; LI, large intestine. Horizontal lines within groups show mean values. Statistical analysis was performed by using two-way ANOVA for comparison of weight loss and virus titers and the log-rank chi-square test for survival curves. The differences in the titers of WT and HA2-K58I viruses in the left lower lung were statistically significant (P < 0.01). Statistical analyses could not be performed to compare WT and K58I groups in tissues where no K58I was detected, including the liver and right upper, middle, and lower lung.